1. Field of the Invention
The present invention relates to an opto-electronic integrated circuit having an optical device and an electronic device, both of which are monolithically integrated, and used in optical fiber communication or the like, and a method of manufacturing the same.
2. Related Background Art
Opto-electronic integrated circuits (OEIC) have been conventionally developed as reception front ends used in optical fiber communications or the like. An OEIC is constituted such that a pin-type photodiode (pin-PD) as a light receiving device and a heterojunction bipolar transistor (HBT) as an electronic device are monolithically integrated on an InP semiconductor substrate.
Such conventional techniques are described in detail in, e g., "IEEE Photonics Technology Letters, vol. 2, no. 7, pp. 505-506, Jul. 1990".
In the conventional opto-electronic integrated circuit, a photodiode layer and a transistor layer are sequentially epitaxially grown on a semiconductor substrate. The transistor layer is then removed from a pin-PD region to form a photodiode layer, and a transistor layer is formed in an HBT region, thereby completing a pin-PD and an HBT, respectively. In this case, the pin-PD is constituted by only the photodiode layer while the HBT is constituted by the photodiode layer and the transistor layer formed thereon.
In general, however, a photodiode layer has a thickness of about 2 to 3 .mu.m, and a transistor layer has a thickness of about 1 .mu.m. Hence, a large step is formed between the pin-PD and the HBT in the direction of thickness. This poses problems on manufacturing such that a resist film is nonuniformly coated upon formation of an etching mask to cause a mask failure, or a metal wiring disposed after formation of devices is disconnected.
In addition, a thicker pin-PD cannot be formed to prevent an increase in step between the pin-PD and the HBT, resulting in low conversion efficiency of received light.
Furthermore, since the resistor in the electronic circuit is formed using an epitaxially grown semiconductor layer, the resistance largely varies with respect to a temperature.